The present invention relates to a rotary compressor and, more particularly, to the control of refrigerating capacity of an air conditioning system employing a rotary compressor.
Conventional rotary compressors of sliding vane type are finding spreading use as compressors of automobile air conditioners since they are compact and simple in construction as compared with conventional reciprocating type compressors which have a large number of parts and are of complicated construction. In comparison with the reciprocating type compressors, however, the known sliding vane type rotary compressors involve the following problems.
Namely, when used as a compressor of an automobile air conditioner, the rotary shaft of the compressor is driven by the driving power of the engine through a clutch having a pulley which is driven by the engine power via a belt. Therefore, with the sliding vane type compressor, its refrigerating capacity is increased substantially linearly in proportion to the speed of the engine.
On the other hand, with the reciprocating type compressor, the follow-up characteristics of its suction valve are degraded at high operation speeds so as not to provide full sucking of refrigerant gas into cylinders. In consequence, the refrigerating capacity levels off when the operation speed of the compressor is increased beyond a predetermined speed. In other words, the refrigerating capacity of a reciprocating type compressor is automatically suppressed during high speed running of the automobile, while such automatic suppressing function is not involved in the rotary compressor. Therefore, with the automobile air conditioner employing the rotary type compressor, an increased compression work results in the lowering of efficiency or in subcooling during high speed running of the automobile.
In order to avoid the above-described problem involved in the rotary compressor, it has been proposed to provide a control valve in a passage leading to a suction port formed in one of the side walls of the compressor, the control valve being adapted to be varied in the opening area of the passage depending upon the engine speed such that the opening area is reduced during high speed operation to cause suction loss which is utilized to control the refrigerating capacity. In this measure, however, a control valve must be additionally provided to thereby make the construction of the compressor complicated and raise the production cost.
As another measure for eliminating the drawback of the rotary compressor, i.e. excessive refrigerating capacity at high speed operation, it has been proposed also to adopt such a construction which includes a fluid clutch, planetary gear system and so forth to prevent the operation speed from being increased above a predetermined speed. In the construction having a fluid clutch, however, energy loss due to generation of heat at relatively moving surfaces is relatively large. On the other hand, in the construction having a planetary gear system, a large number of parts thereof make the size of the compressor large, which goes quite contrary to the current demand for simplification of the compressor and reduction of the size of the same to cope with the requirement of energy saving.